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Current West Nile Virus Information for San Mateo County

2022 Season

West Nile Virus Update

May contain: chicken, animal, bird, poultry, and fowl
District sentinel chickens enjoy a seasonal pumpkin treat.

The District collects and tests dead birds reported by residents. Dead birds should be in good condition without signs of decay or trauma. All bird species are accepted except water fowl, poultry and pigeons/doves.

The California state West Nile virus hotline closed for the season to live calls on October 14. However, residents can still make an online report at District staff will continue to collect and test suitable birds through the winter months.

San Mateo County

October typically marks the end of the West Nile virus season. As of November 1, 2021, there have been 230 dead birds reported in San Mateo County. Of those, 53 have been suitable for testing and all have tested negative for West Nile virus (WNV). No mosquito pools or sentinel chickens have tested positive for West Nile virus in San Mateo County in 2022. Sentinel chicken testing has ended for the year and the chickens are being retired to local properties with coops.


Statewide, 4,581 dead birds have been reported and 1,222 have been tested with 185 positive results (15%). This is lower than last year, when 209 dead birds had tested positive at this date, and well below the five year average of 345 positive dead birds by the end of October. Thus far in 2022, 3,128 mosquito samples have tested positive for West Nile virus from 24 counties. Statewide, 144 sentinel chickens have tested positive from thirteen counties.

In California, there have been 106 human cases of West Nile virus infection, including a case in Santa Clara County. Of these human cases, seven have been fatalities. Most human cases were in the San Joaquin Valley and Los Angeles County.

May contain: plot, chart, and map
Map from


Date last reviewed: November 2, 2022

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